[atlas] Probe areas

Hello, When you start a measurement, you can specify an area to chose probes from. These areas are like "West", "North-Central", "South-East"... What do they corresponds to? If I use the "West" area, this is the west of what? Of the europe? Because "west of the world" barely makes any sense to me, and I can't find any documentation about these areas. I feel like I'm missing something obvious, so I'd be grateful if someone can enlighten me :) Thanks, Yohan